From b30c60d1a54f65ff5638422f1c74e56ac655ec87 Mon Sep 17 00:00:00 2001
From: npeter83 <npeter83+claude@gmail.com>
Date: Sun, 25 Oct 2026 20:48:14 +0100
Subject: [PATCH] feat(nav): each module declares its URL keys; a page switch
 clears them and a page opens without another's

The shell cleared a hand-kept key list on a page switch (it missed the Files and feed keys) and cleared
nothing when a page opened from a link carrying another page's keys. ModuleDef.urlKeys now names every
key a page's view writes, the shell derives both from the registry, and moduleUrl.contract.test holds the
declarations true: one owner per key, no shell key, exactly what each codec writes, and no undeclared
key literal in the app.
---
 docs/development.md                           |   7 +-
 .../NavigationProvider.dom.test.tsx           |  32 +++++
 .../navigation/NavigationProvider.tsx         |  30 ++---
 .../src/features/navigation/moduleRegistry.ts |  11 ++
 frontend/src/lib/channelsUrlState.ts          |   3 +-
 frontend/src/lib/filesUrlState.ts             |   6 +
 frontend/src/lib/moduleDef.ts                 |   6 +
 frontend/src/lib/plexUrlState.ts              |   5 +-
 frontend/src/lib/urlState.ts                  |  19 ++-
 frontend/src/moduleUrl.contract.test.ts       | 125 ++++++++++++++++++
 frontend/src/modules/activity/module.ts       |   2 +
 frontend/src/modules/channels/module.ts       |   2 +
 frontend/src/modules/config/module.ts         |   1 +
 frontend/src/modules/feed/module.ts           |   2 +
 frontend/src/modules/files/FilesProvider.tsx  |   9 +-
 frontend/src/modules/files/module.ts          |   2 +
 frontend/src/modules/home/module.ts           |   3 +
 frontend/src/modules/notifications/module.ts  |   1 +
 frontend/src/modules/playlists/module.ts      |   2 +
 frontend/src/modules/plex/module.ts           |   2 +
 frontend/src/modules/scheduler/module.ts      |   1 +
 frontend/src/modules/settings/module.ts       |   1 +
 frontend/src/modules/stats/module.ts          |   1 +
 frontend/src/modules/users/module.ts          |   1 +
 24 files changed, 246 insertions(+), 28 deletions(-)
 create mode 100644 frontend/src/lib/filesUrlState.ts
 create mode 100644 frontend/src/moduleUrl.contract.test.ts

diff --git a/docs/development.md b/docs/development.md
index 0bb8d445..a81a6349 100644
--- a/docs/development.md
+++ b/docs/development.md
@@ -45,7 +45,9 @@ A frontend page is one folder, `frontend/src/modules/<id>/` (the layering is in
    page renders into the floating header itself through `PageHeader`; the shell knows no page.
 2. `module.ts`: its `ModuleDef` (`lib/moduleDef.ts`): id, label keys, icon, an optional `gate`, the page as a
    `lazyWithPreload(() => import(…))`, and optionally a rail and a `Store`. Of its own folder it imports statically
-   only its store (a `…Provider` / `…Store` file); the page and the rail load lazily.
+   only its store (a `…Provider` / `…Store` file); the page and the rail load lazily. `urlKeys` names every
+   address-bar key its view writes (the URL is the view: a bookmark reopens it), its list kept in `lib/` beside
+   its codec; the shell clears them on a page switch and opens a page without another page's keys.
 3. `index.ts`, the module's public face: the definition, and only what other folders must read (its store's
    hooks). Another folder reaches the module through this file or not at all.
 4. The id in `lib/urlState`'s `PAGES`, and the definition in `features/navigation/moduleRegistry.ts`, in
@@ -58,7 +60,8 @@ A frontend page is one folder, `frontend/src/modules/<id>/` (the layering is in
    returns to `ui/FilterRail`; tsc names each table still missing the new id.
 
 What holds it: `moduleRegistry.contract.test.ts` (every id defined once, from its own folder, lazily),
-`moduleStores.contract.test.tsx` (no store reads another module), the `local/layers` lint rule (imports only go
+`moduleStores.contract.test.tsx` (no store reads another module), `moduleUrl.contract.test.ts` (each URL key
+belongs to one module and matches what its codec writes; no undeclared key literal), the `local/layers` lint rule (imports only go
 down, a module only through its face) and `chunkGuard` in the build (no lazy page on the boot path), plus the
 i18n parity test.
 
diff --git a/frontend/src/features/navigation/NavigationProvider.dom.test.tsx b/frontend/src/features/navigation/NavigationProvider.dom.test.tsx
index 55684824..d21893eb 100644
--- a/frontend/src/features/navigation/NavigationProvider.dom.test.tsx
+++ b/frontend/src/features/navigation/NavigationProvider.dom.test.tsx
@@ -167,6 +167,19 @@ describe("NavigationProvider · setPage's same-page guard", () => {
     expect(window.location.search).toBe("?page=plex&keep=1");
   });
 
+  it("leaves the keys of the modules it does not list by hand behind too: Files and the feed's", () => {
+    // Each module declares its keys (`urlKeys`), and the switch clears the union of them: a key
+    // missing from a hand-kept list rode along onto the next page's entry.
+    window.history.replaceState(
+      { sfPage: "files" },
+      "",
+      "/?page=files&folder=all&item=5&q=music&sort=oldest&keep=1",
+    );
+    const { result } = render();
+    act(() => result.current.setPage("plex"));
+    expect(window.location.search).toBe("?page=plex&keep=1");
+  });
+
   it("pushes nothing when it is already that page", () => {
     const { result } = render();
     act(() => result.current.setPage("plex"));
@@ -195,6 +208,25 @@ describe("NavigationProvider · setPage's same-page guard", () => {
   });
 });
 
+describe("NavigationProvider · a link carrying another page's keys", () => {
+  it("opens with only its own page's keys: what the page does not show, its address does not say", () => {
+    window.history.replaceState(
+      {},
+      "",
+      "/?page=activity&at=logs&folder=all&ctab=hidden&q=music&pscope=movie&pl=3&keep=1",
+    );
+    render();
+    expect(window.location.search).toBe("?page=activity&at=logs&keep=1");
+  });
+
+  it("keeps the channel page open over any page", () => {
+    window.history.replaceState({}, "", "/?page=stats&chan=UC1&folder=all");
+    const { result } = render();
+    expect(window.location.search).toBe("?page=stats&chan=UC1");
+    expect(result.current.channelView?.id).toBe("UC1");
+  });
+});
+
 describe("NavigationProvider · Back", () => {
   // A tab that had a since-removed module open, reloaded onto the new build: its older history
   // entries still name that page, and Back lands on one of them.
diff --git a/frontend/src/features/navigation/NavigationProvider.tsx b/frontend/src/features/navigation/NavigationProvider.tsx
index 37909d56..a09de092 100644
--- a/frontend/src/features/navigation/NavigationProvider.tsx
+++ b/frontend/src/features/navigation/NavigationProvider.tsx
@@ -3,7 +3,6 @@ import { useLatest } from "../../lib/useLatest";
 import { useTranslation } from "react-i18next";
 import { useMe } from "../../lib/useMe";
 import { resolvePage, retiredParams, urlWithParams, type Page } from "../../lib/urlState";
-import { ACTIVITY_KEYS } from "../../lib/activityUrlState";
 import { useDocumentObjectTitle } from "../../lib/documentTitle";
 import { getAccountRaw, setAccountRaw } from "../../lib/storage";
 import {
@@ -13,7 +12,7 @@ import {
   notifyNav,
   rememberNavPosition,
 } from "../../lib/history";
-import { pageTitleKey, reachablePage } from "./moduleRegistry";
+import { foreignUrlKeys, moduleUrlKeys, pageTitleKey, reachablePage } from "./moduleRegistry";
 import {
   channelViewFrom,
   loadInitialPage,
@@ -37,21 +36,13 @@ import {
 //
 // The contexts, their value types and the hooks live in navigationContext.ts.
 
-/** The address bar of `page`'s root: the page (feed implicit) with every view-specific key cleared. */
+/** The address bar of `page`'s root: the page (feed implicit) with every module's own keys cleared — a
+ *  page switch resets to that module's root, and its store mirrors what it holds back in. */
 function pageRootParams(page: Page): Record<string, string | null> {
   return {
     page: page === "feed" ? null : page,
     chan: null,
-    v: null,
-    pl: null,
-    pscope: null,
-    psort: null,
-    pshow: null,
-    pf: null,
-    ctab: null,
-    csort: null,
-    cf: null,
-    ...Object.fromEntries(ACTIVITY_KEYS.map((k) => [k, null])),
+    ...Object.fromEntries(moduleUrlKeys().map((k) => [k, null])),
   };
 }
 
@@ -116,12 +107,10 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
         setAccountRaw(PAGE_KEY, next);
         // Push an in-app history entry so browser/mouse Back steps through pages instead of leaving
         // the app. A fresh { sfPage } (no carried-over _yt/_chan markers) so each page starts at its
-        // root, and the address bar reflects the page (feed is implicit) while clearing the
-        // view-specific params (chan/v/pl and the plex content keys pscope/psort/pshow/pf) — a page
-        // switch resets to that module's root. Feed filters (owned by FeedFiltersProvider) are left
-        // intact; the plex/channels keys re-mirror from PlexProvider / ChannelsProvider on return to
-        // their page. The item it was opened from is still focused: the state setters above have not
-        // re-rendered anything yet.
+        // root, and the address bar reflects the page (feed is implicit) while clearing `chan` and
+        // every module's own keys (pageRootParams) — a page switch resets to that module's root, and
+        // each module's store mirrors its state back in on its page. The item it was opened from is
+        // still focused: the state setters above have not re-rendered anything yet.
         rememberNavPosition();
         window.history.pushState(
           { sfPage: next, sfScroll: nextNavId() },
@@ -244,7 +233,10 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
     // part of the page that replaced it (an `at` tab).
     const linked = new URLSearchParams(window.location.search).get("page");
     const remembered = getAccountRaw(PAGE_KEY);
+    // A link can carry another page's keys (hand-edited, or written by an older build): the page
+    // opens without them, so its address names only what it shows.
     const url = urlWithParams({
+      ...Object.fromEntries(foreignUrlKeys(mountPage).map((k) => [k, null])),
       ...retiredParams(linked ?? (resolvePage(remembered) === mountPage ? remembered : null)),
       page: mountPage === "feed" ? null : mountPage,
     });
diff --git a/frontend/src/features/navigation/moduleRegistry.ts b/frontend/src/features/navigation/moduleRegistry.ts
index 2f557273..82e55d74 100644
--- a/frontend/src/features/navigation/moduleRegistry.ts
+++ b/frontend/src/features/navigation/moduleRegistry.ts
@@ -48,6 +48,17 @@ export const REGISTERED_PAGES: readonly Page[] = ALL.map((m) => m.id);
 
 const BY_ID = Object.fromEntries(ALL.map((m) => [m.id, m])) as Record<Page, ModuleDef>;
 
+// Every module's address-bar keys, and those of every module but `page`: what a page switch clears and
+// what a page opens without (NavigationProvider). Derived from the definitions, so a new module's keys
+// are cleared the day it declares them.
+const ALL_URL_KEYS: readonly string[] = ALL.flatMap((m) => m.urlKeys);
+export function moduleUrlKeys(): readonly string[] {
+  return ALL_URL_KEYS;
+}
+export function foreignUrlKeys(page: Page): readonly string[] {
+  return ALL.filter((m) => m.id !== page).flatMap((m) => m.urlKeys);
+}
+
 // Look up a module's definition by page id (every Page is covered, incl. settings).
 export function moduleDef(id: Page): ModuleDef {
   return BY_ID[id];
diff --git a/frontend/src/lib/channelsUrlState.ts b/frontend/src/lib/channelsUrlState.ts
index 3a0fdd0e..e9e64c3a 100644
--- a/frontend/src/lib/channelsUrlState.ts
+++ b/frontend/src/lib/channelsUrlState.ts
@@ -17,7 +17,8 @@ export interface ChannelsUrlState {
   filters: FilterMap;
 }
 
-const KEYS = ["ctab", "csort", "cf"] as const;
+export const CHANNELS_KEYS = ["ctab", "csort", "cf"] as const;
+const KEYS = CHANNELS_KEYS;
 const VIEWS = ["subscribed", "discovery", "hidden", "blocked"];
 
 // Sort ⇄ `key:dir` (e.g. `subscribers:desc`) via the shared codec in columnSort. There is no default
diff --git a/frontend/src/lib/filesUrlState.ts b/frontend/src/lib/filesUrlState.ts
new file mode 100644
index 00000000..4e964e01
--- /dev/null
+++ b/frontend/src/lib/filesUrlState.ts
@@ -0,0 +1,6 @@
+// The Files page's address-bar keys: the folder shown (`?folder=`, its encoding in
+// modules/files/filesContext) and the file it turns to once (`?item=`). Here, beside the other pages'
+// key lists, so the page's definition can declare them without importing its own folder.
+export const FILES_FOLDER_KEY = "folder";
+export const FILES_ITEM_KEY = "item";
+export const FILES_KEYS = [FILES_FOLDER_KEY, FILES_ITEM_KEY] as const;
diff --git a/frontend/src/lib/moduleDef.ts b/frontend/src/lib/moduleDef.ts
index 207924d7..5bddcdec 100644
--- a/frontend/src/lib/moduleDef.ts
+++ b/frontend/src/lib/moduleDef.ts
@@ -44,4 +44,10 @@ export type ModuleDef = {
   // Static, unlike the page: it is on the boot path by design. It reads no other module's store, so
   // the order the stores nest in does not matter (moduleStores.contract.test).
   Store?: ComponentType<{ children: ReactNode }>;
+  // Every address-bar key this page's view writes: its filters, sort, tab, the item it shows. The URL
+  // IS the view, so a bookmark reopens it. The shell clears them all on a page switch, and opens a page
+  // with no other page's keys in its address (NavigationProvider), so one page's state never rides
+  // along onto another's URL. Empty for a page with nothing of its own in the URL. Each key belongs to
+  // one module and none is a shell key (moduleUrl.contract.test).
+  urlKeys: readonly string[];
 };
diff --git a/frontend/src/lib/plexUrlState.ts b/frontend/src/lib/plexUrlState.ts
index 2b1c5990..c40bc375 100644
--- a/frontend/src/lib/plexUrlState.ts
+++ b/frontend/src/lib/plexUrlState.ts
@@ -18,7 +18,10 @@ export interface PlexUrlState {
   filters: PlexFilters;
 }
 
-const KEYS = ["pscope", "psort", "pshow", "pf"] as const;
+export const PLEX_KEYS = ["pscope", "psort", "pshow", "pf"] as const;
+const KEYS = PLEX_KEYS;
+// The Plex sub-view's key (show, season, info, person… — modules/plex/plexSubUrl encodes it).
+export const PLEX_SUB_KEY = "v";
 const SCOPES = ["movie", "show", "both"];
 const SHOWS = ["all", "unwatched", "in_progress", "watched"];
 
diff --git a/frontend/src/lib/urlState.ts b/frontend/src/lib/urlState.ts
index 486ad5e9..53c269dd 100644
--- a/frontend/src/lib/urlState.ts
+++ b/frontend/src/lib/urlState.ts
@@ -6,7 +6,7 @@
 // the short module/channel name (NavigationProvider owns document.title) — the query never leaks into it.
 import { TAG_CATEGORIES, type FeedFilters } from "./api";
 
-const KEYS = [
+export const FEED_KEYS = [
   "q",
   "show",
   "sort",
@@ -29,6 +29,23 @@ const KEYS = [
   "mindur",
   "maxdur",
 ] as const;
+const KEYS = FEED_KEYS;
+
+// The keys the shell itself reads, whatever page is on screen: the page, the channel page (it opens
+// over any page), the welcome card's mode and the one-time entry links. No module may declare one of
+// these (moduleUrl.contract.test), and a page switch never clears them.
+export const SHELL_KEYS = [
+  "page",
+  "chan",
+  "m",
+  "link",
+  "oauth",
+  "admin",
+  "account",
+  "login",
+  "deleted",
+  "token",
+] as const;
 
 export function filtersToParams(f: FeedFilters): URLSearchParams {
   const p = new URLSearchParams();
diff --git a/frontend/src/moduleUrl.contract.test.ts b/frontend/src/moduleUrl.contract.test.ts
new file mode 100644
index 00000000..f587090f
--- /dev/null
+++ b/frontend/src/moduleUrl.contract.test.ts
@@ -0,0 +1,125 @@
+// @vitest-environment jsdom
+//
+// The URL is the view: each module declares the address-bar keys its view writes (`urlKeys`), and the
+// shell clears them on a page switch and opens a page without another page's keys (NavigationProvider,
+// derived from these declarations). That only holds while the declarations are true, so this pins
+// them: each key belongs to one module and is no shell key, every codec writes only its module's keys,
+// and no key literal anywhere in the app reads or writes the address bar undeclared.
+import { describe, it, expect } from "vitest";
+import { readdirSync, readFileSync, statSync } from "node:fs";
+import { join, relative } from "node:path";
+import { moduleDef, REGISTERED_PAGES } from "./features/navigation/moduleRegistry";
+import { DEFAULT_TAG_MODES, EMPTY_PLEX_FILTERS, type FeedFilters } from "./lib/api";
+import { filterParamUpdates, SHELL_KEYS, type Page } from "./lib/urlState";
+import { channelsParamUpdates } from "./lib/channelsUrlState";
+import { plexParamUpdates } from "./lib/plexUrlState";
+import { activityParamUpdates, DEFAULT_ACTIVITY_STATE } from "./lib/activityUrlState";
+import { DEFAULT_LOGS_STATE, logsParamUpdates } from "./lib/logsUrlState";
+import { FILES_KEYS } from "./lib/filesUrlState";
+import { PLEX_SUB_URL } from "./modules/plex/plexSubUrl";
+import { MODE_URL } from "./shell/welcomeMode";
+
+const SRC = __dirname;
+
+const FEED: FeedFilters = {
+  tags: [],
+  tagModes: DEFAULT_TAG_MODES,
+  channelIds: [],
+  q: "",
+  sort: "newest",
+  scope: "my",
+  includeNormal: true,
+  includeShorts: false,
+  includeLive: false,
+  show: "unwatched",
+};
+
+// What each module's own encoders write, from the encoders themselves. Every module that declares a
+// key has a row, so a new one cannot declare keys its codec does not write, or the other way round.
+const WRITES: Partial<Record<Page, () => string[]>> = {
+  feed: () => Object.keys(filterParamUpdates(FEED)),
+  channels: () =>
+    Object.keys(channelsParamUpdates({ view: "subscribed", sort: null, filters: {} })),
+  plex: () => [
+    ...Object.keys(
+      plexParamUpdates({ scope: "both", sort: null, show: "all", filters: EMPTY_PLEX_FILTERS }),
+    ),
+    PLEX_SUB_URL.key,
+  ],
+  files: () => [...FILES_KEYS],
+  playlists: () => ["pl"],
+  activity: () => [
+    ...Object.keys(activityParamUpdates(DEFAULT_ACTIVITY_STATE)),
+    ...Object.keys(logsParamUpdates(DEFAULT_LOGS_STATE)),
+  ],
+};
+
+function sources(dir: string): string[] {
+  return readdirSync(dir).flatMap((name) => {
+    const path = join(dir, name);
+    if (statSync(path).isDirectory()) return sources(path);
+    return /\.tsx?$/.test(name) && !/\.test\.tsx?$/.test(name) ? [path] : [];
+  });
+}
+
+// Key literals that reach the address bar's QUERY: the keys of an object literal handed to
+// `urlWithParams` / `useUrlMirror`, and a `.get("…")` on the live query.
+function queryKeyLiterals(): { key: string; where: string }[] {
+  const out: { key: string; where: string }[] = [];
+  for (const file of sources(SRC)) {
+    const text = readFileSync(file, "utf8");
+    const where = relative(SRC, file).split("\\").join("/");
+    for (const m of text.matchAll(/(?:urlWithParams|useUrlMirror)\(\{([^}]*)\}/g)) {
+      for (const k of `{${m[1]!}`.matchAll(/[{,]\s*(\w+)\s*:/g)) out.push({ key: k[1]!, where });
+    }
+    for (const m of text.matchAll(
+      /new URLSearchParams\(window\.location\.search\)\.get\("(\w+)"\)/g,
+    )) {
+      out.push({ key: m[1]!, where });
+    }
+  }
+  return out;
+}
+
+describe("module URL keys", () => {
+  const owner = new Map<string, Page>();
+  for (const page of REGISTERED_PAGES) {
+    for (const key of moduleDef(page).urlKeys) owner.set(key, owner.get(key) ?? page);
+  }
+
+  it("belong to one module each", () => {
+    const all = REGISTERED_PAGES.flatMap((p) => moduleDef(p).urlKeys);
+    expect(all.filter((k, i) => all.indexOf(k) !== i)).toEqual([]);
+  });
+
+  it("are never a shell key", () => {
+    const shell: readonly string[] = SHELL_KEYS;
+    expect([...owner.keys()].filter((k) => shell.includes(k))).toEqual([]);
+    // The welcome card's sub-view key is the shell's own.
+    expect(shell).toContain(MODE_URL.key);
+  });
+
+  it.each([...REGISTERED_PAGES])("are exactly what %s's encoders write", (page) => {
+    const declared = [...moduleDef(page).urlKeys].sort();
+    const writes = WRITES[page];
+    if (!declared.length) {
+      expect(writes).toBeUndefined();
+      return;
+    }
+    expect(writes, `${page} declares keys but has no WRITES row`).toBeDefined();
+    expect([...new Set(writes!())].sort()).toEqual(declared);
+  });
+
+  it("cover every key literal the app reads or writes in the address bar", () => {
+    const shell: readonly string[] = SHELL_KEYS;
+    const undeclared = queryKeyLiterals().filter(
+      ({ key }) => !owner.has(key) && !shell.includes(key),
+    );
+    expect(undeclared).toEqual([]);
+  });
+
+  it("the literal scan sees the call sites it is meant to (a regex that matched nothing would pass)", () => {
+    const seen = new Set(queryKeyLiterals().map(({ key }) => key));
+    for (const key of ["chan", "pl", "page", "rjob", "link"]) expect(seen).toContain(key);
+  });
+});
diff --git a/frontend/src/modules/activity/module.ts b/frontend/src/modules/activity/module.ts
index 9eb2347a..fa95fe6b 100644
--- a/frontend/src/modules/activity/module.ts
+++ b/frontend/src/modules/activity/module.ts
@@ -1,6 +1,7 @@
 import { ScrollText } from "lucide-react";
 import { lazyWithPreload } from "../../lib/lazyWithPreload";
 import type { ModuleDef } from "../../lib/moduleDef";
+import { ACTIVITY_KEYS } from "../../lib/activityUrlState";
 
 // This page as the shell and the navigation know it (lib/moduleDef). Its page loads lazily.
 export const activityModule: ModuleDef = {
@@ -12,4 +13,5 @@ export const activityModule: ModuleDef = {
   system: true,
   gate: (me) => me.role === "admin",
   Page: lazyWithPreload(() => import("./Activity")),
+  urlKeys: ACTIVITY_KEYS,
 };
diff --git a/frontend/src/modules/channels/module.ts b/frontend/src/modules/channels/module.ts
index 7e798c40..93b63b8e 100644
--- a/frontend/src/modules/channels/module.ts
+++ b/frontend/src/modules/channels/module.ts
@@ -1,6 +1,7 @@
 import { Tv } from "lucide-react";
 import { lazyWithPreload } from "../../lib/lazyWithPreload";
 import type { ModuleDef } from "../../lib/moduleDef";
+import { CHANNELS_KEYS } from "../../lib/channelsUrlState";
 import { ChannelsProvider } from "./ChannelsProvider";
 
 // This page as the shell and the navigation know it (lib/moduleDef). Its page loads lazily.
@@ -13,4 +14,5 @@ export const channelsModule: ModuleDef = {
   Page: lazyWithPreload(() => import("./Channels")),
   maxWidth: "96rem",
   Store: ChannelsProvider,
+  urlKeys: CHANNELS_KEYS,
 };
diff --git a/frontend/src/modules/config/module.ts b/frontend/src/modules/config/module.ts
index 705322a4..5d0d4b17 100644
--- a/frontend/src/modules/config/module.ts
+++ b/frontend/src/modules/config/module.ts
@@ -12,4 +12,5 @@ export const configModule: ModuleDef = {
   system: true,
   gate: (me) => me.role === "admin",
   Page: lazyWithPreload(() => import("./ConfigPanel")),
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/feed/module.ts b/frontend/src/modules/feed/module.ts
index 51f7a162..3f16fb42 100644
--- a/frontend/src/modules/feed/module.ts
+++ b/frontend/src/modules/feed/module.ts
@@ -1,6 +1,7 @@
 import { YouTubeIcon } from "../../lib/brandIcons";
 import { lazyWithPreload, lazyWithPreloadAlongside } from "../../lib/lazyWithPreload";
 import type { ModuleDef } from "../../lib/moduleDef";
+import { FEED_KEYS } from "../../lib/urlState";
 import { FeedStore } from "./FeedStore";
 
 // The rail loads with the page (lazyWithPreloadAlongside), so it never arrives after it.
@@ -15,6 +16,7 @@ export const feedModule: ModuleDef = {
   Rail,
   Page: lazyWithPreloadAlongside(() => import("./FeedPage"), Rail),
   Store: FeedStore,
+  urlKeys: FEED_KEYS,
 };
 
 // The channel page: a feed scoped to one channel, opened over any page (App renders it in place of the
diff --git a/frontend/src/modules/files/FilesProvider.tsx b/frontend/src/modules/files/FilesProvider.tsx
index 26251199..d2f15fa1 100644
--- a/frontend/src/modules/files/FilesProvider.tsx
+++ b/frontend/src/modules/files/FilesProvider.tsx
@@ -1,6 +1,7 @@
 import { useCallback, useMemo, useState, type ReactNode } from "react";
 import { LS, getAccountRaw, setAccountRaw } from "../../lib/storage";
 import { useUrlMirror } from "../../lib/useUrlMirror";
+import { FILES_FOLDER_KEY, FILES_ITEM_KEY } from "../../lib/filesUrlState";
 import { useNavigation, useNavigationActions } from "../../features/navigation/navigationContext";
 import {
   ALL_FILES,
@@ -33,14 +34,14 @@ import {
 
 function initialView(): FilesView {
   return (
-    parseView(new URLSearchParams(window.location.search).get("folder")) ??
+    parseView(new URLSearchParams(window.location.search).get(FILES_FOLDER_KEY)) ??
     parseView(getAccountRaw(LS.filesView)) ??
     ALL_FILES
   );
 }
 
 function initialFocus(): FilesFocus | null {
-  const id = parseItem(new URLSearchParams(window.location.search).get("item"));
+  const id = parseItem(new URLSearchParams(window.location.search).get(FILES_ITEM_KEY));
   return id === null ? null : { id, token: 1 };
 }
 
@@ -87,8 +88,8 @@ export function FilesProvider({ children }: { children: ReactNode }) {
   const arrived = page === "files" ? arrivedRaw : null;
 
   useUrlMirror({
-    folder: page === "files" ? viewParam(view) : null,
-    item: focus ? String(focus.id) : null,
+    [FILES_FOLDER_KEY]: page === "files" ? viewParam(view) : null,
+    [FILES_ITEM_KEY]: focus ? String(focus.id) : null,
   });
 
   const state = useMemo<FilesState>(
diff --git a/frontend/src/modules/files/module.ts b/frontend/src/modules/files/module.ts
index 4c3d798a..5cef1c49 100644
--- a/frontend/src/modules/files/module.ts
+++ b/frontend/src/modules/files/module.ts
@@ -1,6 +1,7 @@
 import { FolderOpen } from "lucide-react";
 import { lazyWithPreload, lazyWithPreloadAlongside } from "../../lib/lazyWithPreload";
 import type { ModuleDef } from "../../lib/moduleDef";
+import { FILES_KEYS } from "../../lib/filesUrlState";
 import { FilesProvider } from "./FilesProvider";
 
 // The rail loads with the page (lazyWithPreloadAlongside), so it never arrives after it.
@@ -16,4 +17,5 @@ export const filesModule: ModuleDef = {
   Page: lazyWithPreloadAlongside(() => import("./Files"), Rail),
   maxWidth: "80rem",
   Store: FilesProvider,
+  urlKeys: FILES_KEYS,
 };
diff --git a/frontend/src/modules/home/module.ts b/frontend/src/modules/home/module.ts
index cc6c0450..e83cee01 100644
--- a/frontend/src/modules/home/module.ts
+++ b/frontend/src/modules/home/module.ts
@@ -11,4 +11,7 @@ export const homeModule: ModuleDef = {
   icon: Home,
   Page: lazyWithPreload(() => import("./Home")),
   maxWidth: "80rem",
+  // Nothing of its own: the question is an answer, not a setting — the same question draws other
+  // cards once what you have watched moves on.
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/notifications/module.ts b/frontend/src/modules/notifications/module.ts
index bd3072e1..ad05198d 100644
--- a/frontend/src/modules/notifications/module.ts
+++ b/frontend/src/modules/notifications/module.ts
@@ -11,4 +11,5 @@ export const notificationsModule: ModuleDef = {
   hasBadge: true,
   Page: lazyWithPreload(() => import("./NotificationsPanel")),
   maxWidth: "48rem",
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/playlists/module.ts b/frontend/src/modules/playlists/module.ts
index 4fba72dd..fc69335c 100644
--- a/frontend/src/modules/playlists/module.ts
+++ b/frontend/src/modules/playlists/module.ts
@@ -16,4 +16,6 @@ export const playlistsModule: ModuleDef = {
   Page: lazyWithPreloadAlongside(() => import("./Playlists"), Rail),
   maxWidth: "64rem",
   Store: PlaylistsProvider,
+  // The playlist shown (PlaylistsProvider, playlistsInit).
+  urlKeys: ["pl"],
 };
diff --git a/frontend/src/modules/plex/module.ts b/frontend/src/modules/plex/module.ts
index 4d2f9b70..70d36358 100644
--- a/frontend/src/modules/plex/module.ts
+++ b/frontend/src/modules/plex/module.ts
@@ -1,6 +1,7 @@
 import { Clapperboard } from "lucide-react";
 import { lazyWithPreload, lazyWithPreloadAlongside } from "../../lib/lazyWithPreload";
 import type { ModuleDef } from "../../lib/moduleDef";
+import { PLEX_KEYS, PLEX_SUB_KEY } from "../../lib/plexUrlState";
 import { PlexStore } from "./PlexStore";
 
 // The rail loads with the page (lazyWithPreloadAlongside), so it never arrives after it.
@@ -17,4 +18,5 @@ export const plexModule: ModuleDef = {
   Page: lazyWithPreloadAlongside(() => import("./PlexBrowse"), Rail),
   maxWidth: "100rem",
   Store: PlexStore,
+  urlKeys: [...PLEX_KEYS, PLEX_SUB_KEY],
 };
diff --git a/frontend/src/modules/scheduler/module.ts b/frontend/src/modules/scheduler/module.ts
index 0511a3cc..9452e0e7 100644
--- a/frontend/src/modules/scheduler/module.ts
+++ b/frontend/src/modules/scheduler/module.ts
@@ -12,4 +12,5 @@ export const schedulerModule: ModuleDef = {
   system: true,
   gate: (me) => me.role === "admin",
   Page: lazyWithPreload(() => import("./Scheduler")),
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/settings/module.ts b/frontend/src/modules/settings/module.ts
index 551920fc..793c1de8 100644
--- a/frontend/src/modules/settings/module.ts
+++ b/frontend/src/modules/settings/module.ts
@@ -10,4 +10,5 @@ export const settingsModule: ModuleDef = {
   titleKey: "settings.title",
   icon: Settings,
   Page: lazyWithPreload(() => import("./SettingsPanel")),
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/stats/module.ts b/frontend/src/modules/stats/module.ts
index 08e70a6b..9d731d4e 100644
--- a/frontend/src/modules/stats/module.ts
+++ b/frontend/src/modules/stats/module.ts
@@ -10,4 +10,5 @@ export const statsModule: ModuleDef = {
   titleKey: "header.usageStats",
   icon: BarChart3,
   Page: lazyWithPreload(() => import("./Stats")),
+  urlKeys: [],
 };
diff --git a/frontend/src/modules/users/module.ts b/frontend/src/modules/users/module.ts
index 1585f72c..5f34c253 100644
--- a/frontend/src/modules/users/module.ts
+++ b/frontend/src/modules/users/module.ts
@@ -13,4 +13,5 @@ export const usersModule: ModuleDef = {
   gate: (me) => me.role === "admin",
   Page: lazyWithPreload(() => import("./AdminUsers")),
   maxWidth: "48rem",
+  urlKeys: [],
 };